add 'ls-remote' option to limit output records

Given that 'ls-remote' can be sorted, it would be useful to be able to ask for a subset of the total number of result records.

For example, if I want to retrieve only the tag with the highest version, I would do so by adding this new option (-n1 in my example):

	$ git ls-remote -n1 --tags --sort=v:refname origin "v*"

That would save from having to receive a large list of tags from the remote, only one of which I care about.

~David